Surface Fluorination to Boost the Stability of the Fe/N/C Cathode in Proton Exchange Membrane Fuel Cells

Abstract

The ternary Fe/N/C material is a promising non-precious-metal oxygen reduction electrocatalyst for proton exchange membrane cells (PEMFCs). However, its practical application is severely hampered by poor stability under PEMFC working conditions, especially at a cell voltage higher than 0.5 V. Herein, we report a new strategy to significantly improve the stability of the Fe/N/C catalyst in PEMFCs by covalent grafting of a trifluoromethylphenyl (Ar-CF 3 ) group. The hydrophobic character of Ar-CF 3 can effectively prevent water flooding of the Fe/N/ C catalyst layer, and thus form robust mass-transport channels for gasÀliquid two-phase flow. Simultaneously, both electronwithdrawing and hydrophobic properties considerably suppress the oxidative corrosion of the carbon matrix that hosts the catalytically active sites. Therefore, fluorinated Fe/N/C could perform stably over 100 h at 0.5 V with a current density of 0.56 A cm À2 in a H 2 ÀO 2 PEMFC. Even when the cell voltage increased to 0.6 V, only 15 % performance was lost after 100 h operation.[a] Dr.

Fe-N-C catalysts for PEMFC: Progress towards the commercial application under DOE reference

“…As shown in Fig. 9 (a), Zhou and coworkers reported a surface fluorination strategy to improve the stability of the Fe-N-C catalyst in PEMFCs by covalent grafting of a hydrophobic and electron-withdrawing trifluoromethylphenyl (Ar-CF 3 ) group [99] . The electron-withdrawing property can alleviate the oxidative corrosion of the Fe-N-C catalyst, while the hydrophobic property helps to form mass-transport channels in catalyst layer.…”

Effect of Catalyst Layer Hydrophobicity on Fe−N−C Proton Exchange Membrane Fuel Cells

“…Electrode water flooding is a common phenomenon happening in the high current condition in PEMFC, and significantly influences the fuel cell performance. Sun and Zhou et al grafted the hydrophobic and electron-withdrawing trifluoromethylphenyl (ArÀ CF 3 ) onto the FeÀ NÀ C catalyst to reduce the flooding and the carbon oxidation, and the fuel cell durability wad improved with only 15 % reducing of current density after a 100 h durability test at 0.6 V. [7] Dodelet et al [8] proposed a micropore flooding mechanism for the initial fast PEMFC performance decay. But, Choi et al [9] quantified the degree of micropore flooding and opposed the micropore flooding as a major factor for PEMFC performance degradation.…”

Novel Heteroatom-Doped Fe/N/C Electrocatalysts With Superior Activities for Oxygen Reduction Reaction in Both Acid and Alkaline Solutions

“…Among them, carbon-supported nanomaterial with heteroatoms doping (e.g., Co, Fe, N, S, P, and halogens) were widely developed, and they are promising non-precious electrocatalysts to substitute Pt group metal (PGM)-free electrocatalysts for ORR (Gong et al, 2009;Yang et al, 2012;Yao et al, 2012;Zhang and Dai, 2012;Jeon et al, 2013;Chen et al, 2017;You et al, 2018). Sulfur and halogens (F and I) had been introduced as active additives in Fe/N/C or Co/N/C electrocatalysts to improve the electrocatalytic performance (Chen et al, 2015;Nyoni et al, 2015;Wang Y.-C. et al, 2018;Zheng et al, 2019). The dual-doping of non-precious metals (Fe, Co, etc.)…”